This invention relates to protection tubes for the immersion of parameter determining devices into molten metal and more particularly to a non-splash refractory protection tube.
During the refining of metals such as the refining of iron to steel and in the preparation of metals for casting it is essential that certain parameters of the molten metal be accurately and swiftly determined. Some of these parameters are determined by immersing sensing devices into the molten metal that provide electrical signals that are indicative of the magnitude of the parameter. Such sensing devices are used to determine temperature by a thermocouple element, oxygen by an electrochemical cell, and carbon by temperature measurements made as an isolated sample, either in the bath of molten metal or outside the bath, cools through various thermal arrest temperatures. Other parameters of the molten metal require that a sample be removed from the bath of molten metal and be studied by chemical analysis or metallographic analysis. Typical of such parameters are chemical composition and structure.
Parameter determining devices and particularly those that generate electrical signals while immersed in the molten metal are immersed in the molten metal by means of a manipulator consisting of an iron pipe having electrical wires extending therethrough and terminating in appropriate plug-in contact structure at its distal end. During immersion it is essential that the manipulator be physically and thermally protected from the molten metal. In the past this protection has usually been provided by a paper tube of significant wall thickness. Such paper tubes have at least two distinct disadvantages. The paper tube pyrolizes when immersed in high temperature molten metal and thus there is a finite time limit established for the immersion life of the device. Furthermore, the paper tube tends to out-gas and thus produce a hazard to individuals using the devices by causing splashing of the molten metal.
In order to overcome the aforementioned problems a safety sleeve has been used that consists of a metal tube with a castable refractory cement coating applied to the outside of the metal tube. While such a construction eliminated the out-gassing that was present with paper tubes, castable refractory is a relatively poor thermal insulator limiting the useful immersion time of the sensor and, furthermore, such safety sleeves were heavy and expensive.
U.S. Pat. No. 3,816,183 issued June 11, 1974 discusses the problems of the foregoing safety sleeve and proposes an improvement utilizing a paper tube with an outer sleeve made of refractory fibers to provide the non-splash features and the improved thermal insulation necessary to permit more than a single use of a temperature sensing device. The combination of a paper tube and the fibrous sleeve requires that a seal and bond be established between the paper tube and/or the sensor, and the sleeve. Furthermore, the sleeves being made solely of fibrous material and binder have very little mechanical strength and are limited in the lengths available due to the method of manufacture.